The invention relates to chemical mechanical polishing of substrates, and more particularly to a polishing pad with a partial adhesive coating, and to methods and apparatus for producing such polishing pads.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes successively more non-planar. If the outer surface is non-planar, then photolithographic techniques to pattern photoresist layers might not be suitable, as a non-planar surface can prevent proper focusing of the photolithography apparatus. Therefore, there is a need to periodically planarize this substrate surface to provide a planar layer surface.
Chemical mechanical polishing is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head, with the surface of the substrate to be polished exposed. The substrate is then placed against a rotating polishing pad. In addition, the carrier head may rotate to provide additional motion between the substrate and polishing surface. Further, a polishing slurry, including an abrasive and at least one chemically-reactive agent, may be spread on the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
A typical polishing pad includes a hard top layer and a softer bottom layer. The top layer has a high friction polishing surface, capable of transporting slurry, and a second surface adhesively bonded to a first surface of the bottom layer. A second surface of the bottom layer is typically attached to a platen by a high strength pressure-sensitive adhesive layer.
One consideration in the production of integrated circuits is process and product stability. To achieve a low defect rate, each substrate should be polished under similar conditions, i.e., same polishing surface structure. A limitation on process stability, as well as polishing throughput, is "glazing" of the polishing pad. "Glazing" occurs when the polishing pad is frictionally heated and compressed in regions where the substrate is pressed against it, as well as worn as a result of the abrasive contact. The peaks of the polishing pad are pressed and worn down and the pits of the polishing pad are filled up, so the surface of the polishing pad becomes smoother and less abrasive. As a result, the polishing time required to polish a substrate increases. Therefore, the polishing pad surface must be periodically returned to a more uniform abrasive condition, with higher friction and ability to transport slurry. This process is defined as "conditioning" and serves the purpose of maintaining a high polishing rate. The conditioning process can be destructive for the polishing pad and results in reducing the lifetime of the polishing pad. Because of these reasons the polishing pad needs to be removed from the platen and replaced every 100 to 1000 substrates, depending upon the type of substrate and conditioning process.
In order to remove the pad, an operator reaches into the polishing area, grasps the polishing pad by hand or with mechanical aids and pulls it to peel it off the platen. Because of the high strength of the adhesive layer, the operator must apply a large force to pull the polishing pad off the platen. For example, the operator may need to apply pulling force of approximately 100 pounds. This large force can exceed the physical abilities of the operator and can pose a risk of injury.